This proposal involves two polypeptides (Mr ca. 5,000) found in potatoes. One of these inhibits the pancreatic carboxypeptidases, and the other affects chymotrypsin. Amino acid sequence data suggest that the inhibitors may be homologous, and, to further study their similarities, a thorough structural investigation of these molecules is proposed. The amino acid sequence of the chymotrypsin inhibitor and disulfide bond pairing will be completed to afford a comparison with similar information already available on the carboxypeptidase inhibitor. In addition, increased emphasis will be placed on crystallizing these inhibitors and their respective enzyme-inhibitor complexes in preparation for X-ray diffraction studies which will be carried out elsewhere. The second aspect of this proposal is the use of the carboxypeptidase inhibitor to facilitate the preparation of target enzymes. Immobilized carboxypeptidase inhibitor, which has been proven effective in the purification of porcine, bovine, shrimp, and S. greiseus enzymes, will be applied to other systems as susceptible enzymes are identified.